A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an NMR Spectroscopic Probe for the Metal Coordination Environment

Lesueur, William; Solari, Euro; Floriani, Carlo; Chiesi‐Villa, Angiola; Rizzoli, Corrado

doi:10.1021/ic9700819

Cited by 62 publications

(65 citation statements)

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“…This observation is in contrast to one related computational study of PhÀPd insertion into ethene by carbene ligands; for the model (bis)diaminocarbene ligand in 13 weak h 2 -Pd ipso-ortho bonding was observed at the same stage, whilst the monocarbene complex 14 exhibited only PdÀC ortho bonding [17]. There are, in addition, well-established and X-ray-characterised examples of ipso bonding in Pd complexes [18], raising the possibility that this substitution type could be important in Pd catalysis when an aryl ring is in proximity to the catalytic centre. The relative stability of the C ipso ÀPd bond in the present case can be established by introducing a single H 2 O molecule into the coordination sphere.…”

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confidence: 75%

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

Hii

Claridge

Brown

et al. 2001

HCA

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Dedicated to the memory of Professor Luigi M. VenanziReactive intermediates in the asymmetric Heck reaction between aryl electrophiles and 2,3-dihydrofuran have been identified by NMR and mass spectrometry, with BINAP or the achiral diphosphanes dppp and dppf as ligands. The major cationic species observed is an alkylpalladium produced by addition of PdAr to the alkene followed by two further PdH-mediated isomerisation steps. This last species has been characterised at À 608 by 1 H-, 13 C-, and 31 P-NMR, including HMQC techniques. The regiochemistry of PdAr and PdH addition to the reactant are opposite as defined by the reaction with (2-2 H 1 )-2,3-dihydrofuran. DFT Calculations on the reaction pathway between [CH 2 (PH 2 )]PdPh and 2,3-dihydrofuran reveal several structurally interesting intermediates involving agostic b-H-atom, ipso-Ph or reactant O-atom bonded to the Pd-atom, and elucidate the isomerisation pathway.An interesting mechanistic sidelight emerged from the earliest reports of the specified Heck reaction (see [6] and earlier papers cited therein). Depending on the reaction conditions, the product was predominantly the 2,5-or 2,3-dihydro isomer 2 or 3, respectively, with excess PPh 3 providing the latter. This implies an intermediate that can partition between elimination and isomerisation. In the detailed studies carried out by Hayashi and co-workers, both were formed with the latter favored; the enantiomer excess (e.e.) of the major product was enhanced by a favorable partition of the diastereoisomers of the first-formed intermediate, minor towards elimination and major towards isomerisation [5]. Subsequently, Pfaltz and Loiseleur and co-workers demonstrated that catalysis involving a PN ligand in the phosphinoaryldihydrooxazole series provided entirely the 2,5-dihydroisomer in high e.e. [7]; other results obtained were broadly in line with a single double-bond-shift pathway. Subsequent workers have largely confirmed this regiochemical pattern, with diphosphine ligands giving rise mainly to double-isomerisation products and with phosphinamine ligands to singleisomerisation products.When this work was started, there were no detailed mechanistic studies on the asymmetric Heck reaction and, indeed, few on the reaction in general [8]. In the intervening period, there has been an effusion of speculations about the detailed mechanism of simple Heck reactions, especially on the role of Pd 0 ± Pd II vs. Pd II ± Pd IV cycles [9] 4 ), and the possible involvement of deligated colloidal Pd or Pd nanoparticles [10]. Direct evidence on the structure of true late intermediates in the catalytic cycle remains limited to the cationic-diphosphine case from our own work [1] [7] [11] and a related contribution from Akermark and co-workers [12]. There are related studies on alkene-Pd polymerisation or alkene/CO copolymerisation [13] in which comparable intermediates have been identified and characterised. Results and Discussion. ± Observation of Reactive Intermediates. In our original communication on this topic, the o...

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contrasting

confidence: 75%

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

Hii

Claridge

Brown

et al. 2001

HCA

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“…However, an orthogonal synthetic approach based on elaboration of an initially formed triarylmethane scaffold afforded a viable approach to the preparation of (CP i Pr 3 )H on a multigram scale and in reasonable yields. This synthesis of (CP i Pr 3 )H follows an approach inspired by a previously reported synthesis of Ph 2 P( o -C 6 H 4 CH 2 C 6 H 4 - o )PPh 2 , 27 and hinges on the sequential formation and cleavage of two diaryliodonium ions to give the tris(2-halophenyl)methane precursor ( 5 ) (Scheme 1). …”

Section: Resultsmentioning

confidence: 99%

Catalytic Reduction of N₂ to NH₃ by an Fe–N₂ Complex Featuring a C-Atom Anchor

2014

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While recent spectroscopic studies have established the presence of an interstitial carbon atom at the center of the iron-molybdenum cofactor (FeMoco) of MoFe-nitrogenase, its role is unknown. We have pursued Fe-N2 model chemistry to explore a hypothesis whereby this C-atom (previously denoted as a light X-atom) may provide a flexible trans interaction with an Fe center to expose an Fe-N2 binding site. In this context, we now report on Fe complexes of a new tris(phosphino)alkyl (CPiPr3) ligand featuring an axial carbon donor. It is established that the iron center in this scaffold binds dinitrogen trans to the Calkyl-atom anchor in three distinct and structurally characterized oxidation states. Fe-Calkyl lengthening is observed upon reduction, reflective of significant ionic character in the Fe-Calkyl interaction. The anionic (CPiPr3)FeN2- species can be functionalized by a silyl electrophile to generate (CPiPr3)Fe-N2SiR3. (CPiPr3)FeN2- also functions as a modest catalyst for the reduction of N2 to NH3 when supplied with electrons and protons at -78 °C under 1 atm N2 (4.6 equiv NH3/Fe).

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“…These ndings clearly indicated that, in addition to a large bite angle, an ef cient chelating ligand should be composed of fully aryl or alkenyl 37 substituted phosphines. Moreover, the very low reactivity when using the Floriani ligand (β 111 ) 38 (entry 10), which is a methylene linked variant of DPEphos, strongly suggests the importance of the linker oxygen in DPEphos and Xantphos.…”

Section: Development and Optimization Of Platinum Catalysismentioning

confidence: 99%

Platinum-Catalyzed Direct Amination of Allylic Alcohols

Ohshima

Mashima

2012

J. Synth. Org. Chem. Jpn.

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A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an NMR Spectroscopic Probe for the Metal Coordination Environment

Cited by 62 publications

References 45 publications

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

Catalytic Reduction of N₂ to NH₃ by an Fe–N₂ Complex Featuring a C-Atom Anchor

Platinum-Catalyzed Direct Amination of Allylic Alcohols

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A Bidentate Bisphosphine Functioning in Intramolecular Aliphatic Metalation and as an NMR Spectroscopic Probe for the Metal Coordination Environment

Cited by 62 publications

References 45 publications

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

The Intermolecular AsymmetricHeck Reaction: Mechanistic and Computational Studies

Catalytic Reduction of N2 to NH3 by an Fe–N2 Complex Featuring a C-Atom Anchor

Platinum-Catalyzed Direct Amination of Allylic Alcohols

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Product

Resources

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Catalytic Reduction of N₂ to NH₃ by an Fe–N₂ Complex Featuring a C-Atom Anchor